[Vala] Constructors from odd libs (was: Re: canberra.vapi)

["Michael B. Trausch" <mbt zest trausch us>]

On Sat, 11 Jul 2009, Frederik wrote:

> Michael B. Trausch wrote:
> > On Sat, 11 Jul 2009, Michael 'Mickey' Lauer wrote:
> > > Thanks, that's slightly better, still I'd love to have a classical
> > > constructor
> > > way of creating a context, like:
> > >
> > > var c = new Canberra.Context();
> > >
> > > Is this impossible without changes in the library itself?
> >
> > You can (with a bit of work) create APIs that are more object-oriented.
> > You have to do a bit of extra work, though, and the function has to
> > return a pointer to a structure (at least, AFAIK).
>
> In this case the problem is that the function returns the newly
> constructed object as 'out' parameter, not as return value. AFAIK there
> is no 'CCode' attribute for telling Vala to treat an 'out' parameter as
> return value.

Hrm.  That is interesting.  You could write a small C helper that can be 
layered on top of the library's API and help make things fit.  I'm not sure if 
you can, say, call the "real" constructor in a private static function and 
invoke that from Vala code in the constructor for the Compact class, but it 
might be possible.

Another possibility is that there may be some way to tell Vala that the out 
parameter is the newly-created object -- I don't know of a way to do that, 
though, at present.  It is entirely possible that Jürg or someone else will 
know, though; I've updated the subject line to better describe the 
conversation and maybe someone will see it and think of something.  If it 
isn't possible at all at present, maybe filing a feature request asking for an 
attribute to make the mapping work would be best.

        --- Mike